My t does as she feels appropriate for the client and situation. She does a lot of trauma work, so she probably has an easier time by allowing contact. She does put limits on it though: she only responds as ahe is able, and only if it doesn't interfere with whatever she's doing. I'm guessing the only exception to that would be an emergency situation...
I don't think she offers it to all her clients, but she's pretty open about it, at least with me and a few of the other trauma clients of her's (she's mentioned she is more restrictive about it with clients that may be disrupted by the open contact policy)... i also try to be really mindful of when and why i contact her.